Carrier-wave signaling system



Dec. 15, 1925- 1,566,012

- J. W. HORTON CARRIER WAVE SIGNALING SYSTEM Filed Dec. 3, 1920 Patented Dec. 15, 1925.

UNITED STATES PATENT 0 1,566,012 FFICE,

JOSEPH W. HORTON, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK. N. Y.. A CORPORATION OF NEW YORK.

CARRIER-WAVE SIGNALING SYSTEM.

Application filed December 23. 1920. Serial No. 432,647.

To all w7wm it may concern:

Be it known that I, Josnrrr W. Hon'ron,

a citizen of the United States of America,

This invention relates to carrier wave sig- ,nalin systems and more )articularly to a modu atin arrangement or suchsystems.

In signa ing systems of the above general type it is customary, to combine the signaling currents and the carrier wave in such a way that the carrier wave as transmitted to the line is. modulated in accordance with the signaling current. This may well be done in a modulating device of any known type, such, for example, as a magnetic modulator or a thermionic discharge device. In any case, both the signaling current and the carrier wave are impressed upon the input circuit of the modulator and unless some precaution is taken the carrier wave will react upon the signaling current input circuit and may cause distortion and-other undesirable effects.

It is an object of this invention to provide a modulating arrangement whereby such reaction is prevented. Another object is to accomplish this result by means of a simple and cificient device.

These objects are accomplished by using a balanced transformer between the carrier wave and signaling current sources and the input circuit of the mmlulator. The current from each sourceis impressed upon the input circuit ot the modulator conjugatcly with respect to the other source. This arrange ment provides a simple and reliable system, which is valuable from an economic standpoint.

For clcar'ncss of description it may be stated that, the term conjugate transformer as used herein signifies any transformer having a plurality oil? input connections, so related to each other that energy impressed upon any one of those connections will not appear at another. From this it follows that a source of electrical energy is conjugatcly connected with respect to another source to an electrical device when energy from the first mentioned source has no eifcct upon the second mentioned source and vice .versa.

. A special ty e of conjugate t. ansformer 1s a so -called ybrid coil. A hybrid coil comprises two windings, inductively related to each other. One winding may be called a series Winding and the other, a line windmg. In series with the line winding are two equivalent impedances. Connections,- known as bridge terminals, are made to this series circuit in such manner that two paths are provided for the passage of-current, a

portion of the line winding being included n each path. The relation between the two nnpedances and the portions of the line winding in the two circuits is such that,

when a potential is impressed upon this divided circuit, the resultant E. M. F, induced in the series winding is zerol Conversely for any current flowing in the series winding, the E. M. F. across the bridge connection is zero.

A modified form of hybrid coil, herein called a balanced hybrid coil comprises three windings, inductively related to each other. One winding may be called a series winding and the -other t\vo,line windings. Tapped ofi fromnn intermediate point of each line winding is a bridge circuit. The relation of these windings is such that, when the proper values of impedances are 0011-.

nectcd across the several terminals, energy impressed upon the series winding will not affect the bridge circuit and vice versa.

For a further description of hybrid coils r'cfcrcuce may be had to an article by Messrs. Ghcrardi and Jewett entitled Telephone repeaters published in the Proceedings of the American Institute of Electrical Engincers, Volume XXXVIII, No. 11. October, 1919.

The objects hereinbefore mentioned and the means of attaining them will appear more clearly from the description now to follow, when read in connectiorrwith the accon'ipanying drawing. In the drawing the invention is shown'in one embodiment as applied to amultiplex carrier wave tele phone system.

One complete two-way channel for the i'I'iIllSll'llSSlOIl and reception of signals between a low frequency terminal station A. and a main transmission line ML is shown. Station A may represent a toll terminal station, an ordinary telephone exchange'or a subacribers station. This complete channel comprises a receiving circuit RC adapted to receive high frequency signals incoming from the main line ML and to convert them into low frequency signaling current for transmission to the terminal station A and a transmitting circuit TC adapted to receive signaling current incoming fro-m the station A and to convert it into high frequency signals for transmission to the main line The receiving circuit RC may comprise a receiving band filter HBF, a detector D, a detector amplifier DA and a low pass filter LPF. This-receiving circuit may be connected-to the main line ML through a balanced transformer 5 and to the terminal station A through the line L and balanced transformer 6.

The transmitting channel TC may comprise a signaling circuit S which includes an audio frequency transformer 7, a modulator M. an oscillator O, a conjugate transformer BT 'and a modulator band filter MBF. This transmitting circuit is likewise connected to the main line ML through the conjugate transformer 5 and to the low frequency line L through the conjugate transformer 6.

Band filters RBF and MBF are adapted to transmit a broad band of frequencies essential to speech transmission and at such a point in the carrier frequency range as has been selected for that particular transmission channel. The low pass filter LPF is adapted to pass all frequencies below and including the highest essential frequency for voice transmission. These filters may be of the general type described in Campbell patent No. 1,227,113 patented May 22, 1917.

Conjugate transformers 5 and 6 may be the so-called balanced hybrid coils hereinbcfore defined. The hybrid coil 5 has two line windings 8, S) and a series winding 10. It also has four pairs of terminals 11, 12, 13 and 1-1-. Terminals 13 are known as the bridge circuit terminals. Hybrid coil 6 has corresponding terminals 15, 16, 17 and 18. Connected to the terminals 12 and 16 are balancing networks HF N and LFN adapted to balance respectively the main line ML and the low frequency line L.

The carrier waves for the transmitting circuit TC are supplied by the oscillator O. This oscillator may be of any well-known type. The type shown comprises a three electrode thermionic discharge device having its output and input circuits inductively related. The generated energy is available through a potentiometer 19 at the terminals 20. The modulator M may also comprise a three electrode thermionic device having a cathode 26, an anode 25 and an impedance controlling element or grid 24. This device operates to transmit carrier currents modulated in accordance with signaling currents when both high frequency carrier cur-' rent and signaling current are impressed upon its input circuit in a well-known man ner. I

According to this invention a conjugate transformer ET is connected between the modulator M, the oscillator O and the signaling circuit S in such a way that the carrier current from oscillator 0 cannot react upon the signaling circuit S. The conjugate transformer BT as shown in the drawing is a balanced hybrid coil having two line windings 27, 28 and a series winding 29. The line windings terminate in terminals 21 and 22; the bridge circuit, in terminal 23 and the series winding, in terminal 2 Carrier oscillations are supplied to the series Winding 29 at terminal 20 and signaling current, to the bridge circuit at terminal 2 1. Line terminals 21 are connected to the input circuit-grid and cathode circuit of the modulator M while the terminals 22 are connected to a network N. Across the input circuit of the modulator is connected a variable resistance 30 of such value that the impedance between line terminals 21 is substantially constant under all service conditions. The network N is of such a value as to substantially balance this impedance.

While one two-way channel only of a carrier wave signaling system has been shown, additional channels may be added by connecting their receiving and transmitting circuitsas indicated respectively by broken line ci'rcuits 31 and 32.

Batteries and 34 supply respectively the necessary current for heating the cathodes of the thermionic discharge devices and the energy for the plate circuits thereof in a well-known manner.

The operation of such a system for the reception of signals incoming from the main line ML is well-known and will not be further described.

Regarding the transmission of signals according to this invention incoming signals from station A over the line L are trans mitted from the series winding 18 of hybrid coil 6. through the transformer 7 to the bridge terminals 23 of the balanced transformer or hybrid coil RT. The impedances across the several terminals 20, 21, 22 and 23 are so adjusted that the energy supplied at the bridge terminals 23 does not affect the series circuit at the terminals 20. Likewise the carrier oscillations supplied by the generator 0 do not affect the speech circuit connected to terminals 23. Energy from both sources, however, is available at terminal 21. and therefore is impressed upon the input of the modulator M. Carrier current modulated in accordance with signaling current is therefore transmitted from the output of the modulator, through the transformer 35 and modulator band filter MBF to the main line ML.

One embodiment only of the invention has been shown and dcscriheifl. Other ways of applying the invention will be evident to those skilled in. the art. All embodiments as defined by the appended claims, come within the scope of the invention.

, \Vhat'is claimed is:

1. In a modulating systcu'i having a modulator with a single pair of input terminals and a source of carrier waves and a source oi telephone current both connected thereto to impress current thereupon, the method of preventing 'reaction between said sources which comprises impressing the current from each of said sources upon said modulator conjugately with respect to the other of said sources.

2. In a modulating system having a modulator with a single pair of input terminals and a source of carrier waves and a source of signaling current, both connected thereto to impress current thereupon, the method of reventing reaction between said sources w ich comprises impressingv the current from each of said sources upon said modulator conjugately with respect to the other of said sources.

In combination, an electron discharge device, an input circuit thereforhaving two input terminals, and two sources of waves connected in common to said terminals and conjugately with respect to each other.

4. In combination, an electron discharge device, an input circuit therefor having two input terminals, and independent sources of signaling current and carrier waves connected in common to said terminals and conjugately with respect to each other.

5. A modulator, a source of carrier current, a source of signaling current, and a balanced hybrid coil connected tosfid modulator and having terminals conjfigate toeach other, said sources eing connected to said conjugate terminals whereby the carrier current source is prevented from reacting upon the signaling current source.

6. Modulating apparatus comprising 'a device having a single input circuit for translating low frequency signaling current into modulated high frequency oscillations, a circuit to supply signaling current to said device, another circuit to supply high frequency energy; to said device, and a conjugate transformer in circuit between the input circuit of said device and each of said circuits.

7. In a carrier wave signaling system, a

source of carrier waves, a source of signal-' ing current, a modulating device and. a balanced hybrid coil connected between said sources and between each said source and said modulating device.

8. In a carrier wave signaling system, a

source of carrier waves, a source of signaling current, modulating apparatus comprising current, a modulating device, a hybrii coil connected between said sources and. between cach said source and said modulatim, device, and an impedance connected across the input of said modulating device of such a value that the impedance connected across one terminal of the line windings of said hybrid coil is substantially constant.

11. In' a carrier wave signaling system, a source of carrier waves, a source of signaling current, a modulating device, a hybrid coil comprising series and line wind ings and a pluralit of pairs of terminals therefor, said hybrid coil being connected between said sources and between each said source and said modulating device, and substantially e ual resistances connected across each pair 0 terminals of the line windings of said hybrid coil. v

12. In a carrier wave si naling system, a source of carrier waves, a source of signaling current, a modulating device, a hybrid C011 comprising series and line windings and aplurality of pairs of terminals therefor, said hybridcoil being connected between said sources and between each said source and said modulating device, and substantially equal impedances connected across each pair of terminals of the line windings of saidhybrid coil.

13. A conjugate transformer having a plurality of terminals, a modulator connected to one of said terminals, a balancing network connected to another of said terminals to balance said modulator, and a source of carrier waves and a source of signaling current each connected to said conjugate transformer and adapted to supply current to said modulator.

14. A modulator havingga pair of terminals, a h brid coil having a series winding and a bri go circuit, abalaneing network 

